A day's length is set by how high the noon sun climbs, and that height tracks the sun's slow drift north and south across the year. Picture that drift as a swing: at the equinoxes the sun is racing through the middle of its arc, gaining or losing ground fastest, and the day stretches by about four minutes every twenty-four hours. At the solstice the sun reaches the top of the swing and, for a moment, hangs — its north–south motion slows to nothing before it reverses. The day length, riding on that motion, hangs with it.
So the change from one day to the next collapses. In London the day is growing by just — right now, against — back in March — roughly — slower. You could not feel the difference between today and three days from now with the best clock in your kitchen. That flat top is the whole reason the word exists: sol (sun) + sistere (to stand still). The ancients who built stone alignments to catch the solstice weren't marking a single sunrise — they were marking the only week the sunrise stops moving long enough to pin down.
The flatness is universal but its height is not. Step toward the pole and the swing grows: Reykjavík vaults to over twenty-one hours of daylight, and a little farther north Tromsø runs clean off the top — the day hits a full twenty-four hours and simply stays there, the curve clipped into a flat ceiling for weeks. Step toward the equator and the swing shrinks to nothing: Singapore sits at twelve hours and twelve minutes all year, which is why the tropics have no real seasons of light. Same sun, same standstill — the only thing latitude changes is how tall the plateau stands.
daylight_duration, computed from solar geometry; forecast endpoint for the solstice window and the archive (ERA5) endpoint for the March equinox rate. Five locations, UTC. Fetched fresh on load and every thirty minutes. "Solstice" is the day of maximum daylight in the northern series.